1. Field of the Invention
The present invention relates to the dynamic sizing of queues. More particularly, the present invention is directed to the resizing of queues in a network switch device.
2. Art Background
Computer network devices typically include queues that function to buffer incoming and outgoing data that pass through the different ports of a switch. The amount of data passing through the different ports of the switch can vary quite dramatically. In order to accommodate the various bandwidths encountered, the queues may be structured to accommodate an expected maximum bandwidth. However, in such a structure, a large portion of the queues remain unused as the situations that cause the maximum bandwidth utilization of the queue are infrequent. Some systems, therefore, set the queue size to accommodate some expected median bandwidth. However, problems immediately occur when the actual bandwidth exceeds the expected median.
An inadequate size may have severe performance implications for the entire switch. For example, in the many-to-one situation, the traffic patterns crossing the switch are such that several input ports need to forward data to one output port. This may cause a temporary congestion on the output port. Similarly, in a one-to-many situation, multi-cast traffic that arises from the input port may need to be forwarded to many output ports. This may cause traffic multiplication and again result in temporary congestion on an output port. In still another situation, a fast input port may forward traffic to a slow output port. This again will result in temporary congestion at the output port.
In addition to the problems caused by temporary congestion, other network requirements may cause other problems. Switches may need to provide multiple output queues per port in order to be able to support some of the quality of service (QOS) features, such as traffic type prioritization, traffic type discarding policies when one or more of the queues fill up and support for protocols that allow for bandwidth reservation and allocation such as RSVP (ReSerVation Protocol). Thus, it is desirable to provide a flexible mechanism that provides for dynamic tuning of the number and sizes of the output queues in a high performance switch network element without disrupting network services.